Electromagnetic Interference (EMI) is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. In power tools, EMI can be radiated by motor terminals, lead wires, and brushes. In particular, in brushed motors, where commutation of the armature is accomplished as a result of contact between the brushes and the commutator bars, EMI can be substantial. In brushed motors, as contact is made and broken during commutation, the energy in the windings has to dissipate due to the abrupt changes in the windings' current. This energy is then coupled with nearby wires and other metal parts, which act as antennae (depending on the frequency) to radiate the electromagnetic energy. This energy may cause electromagnetic interference with other components in the vicinity of the power tool.
Various EMI suppression components (hereinafter also referred to as “EMI components”) may be utilized to reduce the EMI generated by power tool motor components. Capacitors are exemplary components used as EMI components. The challenge faced by power tool design engineers is how to use the smallest and/or least amount of EMI components effectively to meet the regulatory EMI requirements. The contact between the motor commutator and brushes typically generate the most EMI, but mounting the EMI suppression components in the vicinity of the motor commutator and the brushes is often challenging. Moreover, EMI components need to be properly grounded to reduce emissions. In framed motors where the motor is contained inside a metallic housing, the EMI components may be grounded to the motor frame. In frameless motors, however, proper grounding of the EMI components presents additional challenges. What is needed is a cost and space effective EMI suppression mechanism in a power tool.